Systems for supplying fuel to gas turbine engines have used positive displacement or multiple pump systems. A recognized improvement to such fuel delivery systems is the use of a single main centrifugal fuel pump because of the simplicity of the pump, a resulting lower weight system and improved reliability, all of which are important for fuel supply to aircraft gas turbine engines. When the centrifugal pump is driven in a fixed ratio to the speed of the engine, a problem arises in that the centrifugal pump, at a relatively low speed, will deliver a substantial flow of fuel, but the delivered fuel is not at adequate pressure to achieve engine nozzle pressure for engine-starting and running conditions.
Proposed solutions for delivering fuel to the engine at start-up have included the use of an intermittent duty pump, either mechanically driven through some type of decoupling mechanism, such as a clutch, or an electric motor, so that the intermittent duty pump can be effectively removed from the system by declutching the drive or switching off the motor. These solutions have disadvantages in that the system is increased in complexity with resulting reduction in overall reliability because of the additional power source and the mechanisms required. It is also known to have a charged accumulator in the system which can discharge fuel at an increased pressure upon start-up.
Adequate pressure could be delivered by increasing the size of a centrifugal pump but this would provide excess fuel flow and waste of power.